public NBodySystem() {
bodies = new Body[] {Body.sun(), Body.jupiter(), Body.saturn(), Body.uranus(), Body.neptune()};
double px = 0.0;
double py = 0.0;
double pz = 0.0;
for (int i = 0; i < bodies.length; ++i) {
px += bodies[i].vx * bodies[i].mass;
py += bodies[i].vy * bodies[i].mass;
pz += bodies[i].vz * bodies[i].mass;
}
bodies[0].offsetMomentum(px, py, pz);
}